Category Archives: biodiversity

From Thorn to Orchid

Last Summer I got to revisit an old haunt in South London where I used to volunteer with the London Wildlife Trust. I was very excited about returning to Hutchinson’s Bank Nature Reserve (it is in the suburb of New Addington and easily reached by tram from Croydon). I left the restoration project when I moved ‘North of the River’ some years ago and had not seen the final transformation from scrubland back to chalk grassland. I was not disappointed – this site is a bit of a treat even when the weather isn’t at its finest.

The reserve was taken on by LWT (on behalf of Croydon council) because of the potential to enhance the scrubbed over chalk grassland through habitat restoration & management work and by building on the planting and maintenance already undertaken by a group of dedicated locals who had successfully introduced small patches of Kidney vetch (Anthyllis vulneraria) and Greater yellow rattle (Rhinathus angustifolius). Because of these locals who were actively involved there was also already a very impressive list of butterfly and orchid records associated with the site.

Lowland calcareous grasslands form over shallow limestone-rich or chalky soils which have a typically high pH, low nutrient levels and tend to be free draining. Because they favour these particular conditions, chalk grassland plant species are called calcicoles (lime-loving plants). Much of Hutchinson’s Bank Nature Reserve is, as the name implies, on the slope of an embankment which aids with the drainage of rainfall, and the fact that the slope is south-facing ensures fairly warm conditions throughout the Summer months.

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Clockwise from top left: Tibellus oblongus; mating Robberflies, Machimus atricapillus with prey; Longhorn beetle, Rutpela maculata; Marbled white, Melanargia galathea on scabious; Small Blue, Cupido minimus on Anthyllis vulneraria; Pyramidal orchid, Anacamptis pyramidalis; Volucella pellucens; Philodromus sp.; Chrysotoxum bicinctum; Oncocera semirubella; Roesel’s Bush Cricket, Metrioptera roeselii.

It is estimated that there is between 25,000 ha and 32,000 ha of chalk grassland in the UK1 where it is considered a nationally rare habitat. Calcareous grasslands have been described as being equivalent to coral reefs in terms of their species richness, and though this can be seen in small areas, the comparison doesn’t really hold once you increase the scale of the compared areas. As you increase the study area on a coral reef, you will continue to find new species at a higher rate than in chalk grasslands where you will fairly quickly find all the resident species, relatively speaking.

This notwithstanding, calcareous grasslands are highly species rich with a single square metre supporting between 50 and 60 species of vascular plant (including 37 Red Data Book species). As a result of this habitat heterogeneity, we find variation in vegetation structure and large numbers of different food plants which cater for one of the most diverse insect communities in Britain.2

What makes these habitats especially rare is the fact that they are remnants of Mesolithic  agriculture; established about 9,500 to 5,000 years ago when forest cover was cleared for growing crops and rearing domestic animals which continued well into the Neolithic era. The highly porous soils meant that nutrients leached away and that these largely-unfertilized fields eventually lost productivity and were abandoned for new sites. But while they were productive, they were kept clear of encroachment by scrub and the succession to closed-canopy forest was inhibited.2, 3, 4 These cleared areas would then support grass swards and herbs associated with both steppe and Meditteranean vegetation types whose seeds had previously lain dormant in the soil seed bank. This anthropogenic land management system involves quite a specific regimen, and though supported by some historical pollen records and fossilised beetle fauna, it remains unresolved.4, 5 

In 2000, Frans Vera proposed a new hypothesis to explain open patches of land (much like savannahs) based on the same evidence but concluded that these areas were maintained by large herbivores such as auroch, wild horses and deer. The Vera Hypothesis, as it has come to be known, remains controversial and has become the basis for a large-scale rewilding experiment at Oostvaardersplassen in the Netherlands. It is likely, in my view, that a mosaic of open areas was first created for agricultural use and then maintained by browsing and grazing of ungulates.

With this in mind, it is therefore interesting to view a map of Hutchinson’s Bank Nature Reserve from 2012 which shows the management plan for different areas including removing topsoil (the most recent land use was modern agriculture, rotational grazing and cutting back scrub. These accepted chalk grassland management practicesare very similar to those used by Mesolithic farmers ~9,000 years ago.

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London Wildlife Trust map and management plan for Hutchinson’s Bank Nature Reserve from 2012.

The largest threat to chalk grassland ecosystems is therefore a lack of correct management which leads to encroachment of scrub and eventually reforestation. Add to this past (and perhaps recurring) socio-economic pressures to develop high-yield crops and provision of housing, and the threat becomes compounded. With only 29% of lowland calcareous grasslands assessed as SSSI being described as favourable by the Joint Nature Conservation Committee, there is real cause for concern. However, an additional 40% of sites are described as “unfavourable recovering”, but without any indication of what that means for each site in terms of actual improvement over time I am unsure of how much solace one can draw from that number.

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Female larva of the nationally scarce Drilus flavescens that I found at Saltbox Hill SSSI in 2011.

It was on one of my volunteering days in August 2011 that we went to another chalk grassland managed by LWT nearby. We were here to survey the vegetation, plot the exact perimeter and identify areas for habitat management.

Saltbox Hill SSSI is located near Biggin Hill airport and is on a very steep hillside with ancient woodland on the ridge of the hill. With an impressive species list and located near the home of Charles Darwin, this area undoubtedly has natural history kudos, and it was here that I found one of the strangest looking insects that had me puzzled for quite some time.

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NBN atlas map showing the distribution of Drilus flavescens in the UK.

 

Some small square sheets of corrugated iron had been set out to act as refugia for the resident slow worms and snakes. Sitting on the edge of one of these sheets was a segmented, rather hairy, caterpillar-like insect. I was completely stumped. I just about managed to get a photo with my phone and as soon as I got home I turned to the internet for help. iSpot is a very useful resource for these baffling discoveries – experts and amateurs alike will help with an ID of any species from a photo and some habitat information. Within a matter of hours I had an ID of Drilus flavescens. Turns out my insect was the female larva of a highly sexually dimorphic beetle found in chalk grasslands. It has a very limited range and is classified as scarce in the UK. Fascinatingly, the males look more like traditional beetles as adults, while the females remain looking much like their larval form. You can find more information at Mark Telfer’s excellent website here.

A visit to a chalk grassland in Summer is a complete sensory immersion. I implore you to go and walk through the grasses skirting the ant mounds; smell the heady herby scents of wild thyme and oregano as you brush past; be surrounded by the buzzing of bees and flies and the soft susuration of grasshoppers; and be dazzled by the sight of brightly-coloured flowers and dancing butterflies. These are spaces that celebrate the wonder of life. I am heartily looking forward to another visit this year.

 

References:

  1. Price, E.A.C. (2003) Lowland Grassland and Heathland Habitats (Habitat Guides Series), Routledge, London and New York.
  2. Mortimer, S.R., Hollier, J.A. and Brown, V.K. (1998) Interactions between plant and insect diversity in the restoration of lowland calcareous grasslands in southern Britain. Applied Vegetation Science 1: 101-114.
  3. Willems, J.H. (1983) Species composition and above ground phytomass in chalk grassland with different managementVegetatio, 52, 171-180.
  4. Robinson, M. (2014) The ecodynamics of clearance in the British Neolithic. Environmental Archaeology. 19 (3), 291-297
  5. Bush, M.B. and Flenley, J.R. (1987) The age of the British chalk grassland. Nature329 (1), 434-436.
  6. Butaye, J., Adriaens, D., and Honnay, O. (2005) Conservation and restoration of calcareous grasslands: a concise review of the effects of fragmentation and management on plant species. Biotechnologie, Agronomie, Société et Environment. 9 (2).
  7. Crawshay, L. (1903). On the life history of Drilus flavescens, Rossi. Transactions of the Entomological Society of London, 51, 39 – 51.

 

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Marshland meander: A visit to RSPB Rainham Marshes

I have been a card-carrying member of the Royal Society for the Protection of Birds for about 15 years. In that time I have seen some great successes and a variety of challenges faced by the society. The RSPB is the largest nature conservation charity in the UK (with over 1 million members) and also the oldest. Originally set up in 1889 by a group of women who were concerned about the hunting of birds for their feathers (which were a la vogue – especially the decorative use of grebe skins and egret plumes in the hats of Victorian ladies).

The ‘Birds’ component of the RSPB’s moniker is still very relevant today as they continue to work on species protection projects that focus on individual UK bird species which are in decline or under threat such as stone curlews, black-tailed godwits, corncrakes and lapwings.  In fact this strategy proved highly successful in the past as with the red kite re-introduction project which saw numbers of a globally threatened species rise to 1,800 breeding pairs in Britain between 1980 and 2011. This methodology has, however, led to some criticism of the single-species approach for tending to select high-profile charismatic species, and employing management practices that may disadvantage non-target species. It also raises the question of why a particular species should receive conservation preference over any other. To this end the IUCN Red List of Threatened Species was established to help assess the conservation status of species by identifying threatened species and promoting conservation action. We aren’t even aware of the totality of extant species, nor do we have a full understanding of which of those are, or me be, under threat. Insects are a good example; with only 6,051 insect species listed in the IUCN Red List database (of somewhere between 1 million known species and up to 8.5 million expected to be found) there is still an enormous amount of work to be done.

The RSPB’s conservation work, does however involve more than the protection of individual species. Another component of this work is habitat management which is undertaken at more than 200 reserves maintained by the society. This presents the RSPB with opportunities to work towards conserving other (unfeathered) species either on their own or in collaboration with partner organisations. At a time when environmental protections in the UK are likely to be significantly eroded and underfunded, there is some small comfort to be drawn from the fact that there are many conservation organisations like the RSPB that will continue to work to maintain, manage and support wildlife and wild places. But conservationists will need to be focused and their priorities will need to be very clear.

In 2013 the RSPB added the tagline “Giving nature a home” to its logo exemplifying how it has become a conservation charity that now also focuses its attention on wild spaces and the plight of all the other featherless organisms. Though this could be seen as a large charity cannibalising and intervening in the work of smaller (and more focused) organisations in the sector, the sheer scale and associated land-area that the RSPB maintains does allow for a more holistic approach with regards ecosystem and habitat conservation – effectively creating opportunities for protecting and conserving a wide range of species through landscape-level management. What is significant here, though, is that we need to be able to maintain an interesting matrix of connected habitats of varying sizes in order to be able to support as much biodiversity as possible.

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RSPB Rainham Marshes is one of the reserves in the society’s portfolio which was established in 2000 in an area of Essex along the river Thames that was formerly Ministry of Defence land and closed to the public for over 100 years. Part of the Inner Thames Marshes SSSI that stretches over an area of 479.3 hectares this area is a haven for wetland birds. On my recent visit I got to see some of these including swans, lapwing, oystercatcher, marsh harrier, shoveler, shelduck, mallard, canada geese, little grebe, grey heron, redshank, sedge warbler, reed bunting, as well as swifts, linnets, goldfinches, kestrel, sand martins and a displaying skylark. Hauled out on a sandbar on the far bank of the river was a group of 7 harbour seals. As fantastic as these were, why I really came to Rainham was for the invertebrates. The low-lying grazing marsh with wet grassland, ditches, scrub and reed beds on an urban and light-industrial fringe make for a complex habitat mix with a number of interesting ecotones.

It was for the most part a beautifully sunny afternoon, but quite windy at times making some of the photography quite challenging (as you’ll notice from a few rather blurry shots in the following slideshow). I’ve also made note of a few additional butterflies that I was just too slow to photograph – small heath, large white, peacock, red admiral and large skipper – as well as a broad-bodied chaser that zoomed past my head.

All of the invertebrates featured were found through observation and searching by hand because I wanted to photograph them as undisturbed and in as natural a setting as possible. This has meant that species that would have been found by using a pooter, sweep net or beating tray are lacking from my finds. Nonetheless, I was delighted with the dazzling green of the swollen-thighed beetle (Oedemera nobilis) perfectly placed at the heart of a dog rose its femurs bulging like metallic pantaloons, found quite soon after leaving the visitor centre. A leisurely walk along the bank of the river skirting the reserve presented many empid flies, jumping spiders, bumble bees and my first record of a knobbed shieldbug (Podops inuncta) scuttling for cover across a concrete embankment where I chose to stop for my ploughman’s lunch.

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Please feel free to send me corrections if I have misidentified anything or if you can get closer to species with those I’ve only managed to identify to genus.

I then cut away from the river, crossing a channel of pebbles and loose rock aggregate where a  mix of stonecrop, bramble and ragwort pushed up through the gaps. Here were more bees and another personal first of  a couple of black-striped longhorn beetles (Stenurella melanura) on bramble flowers. This area also had a scattering of detritus washed up from the river: bits of plastic, wood, a child’s sky-blue bicycle lying on the mudflat.  Beneath a plank I found a scuttling centipede and a cluster of earwigs all with abdomens raised and forceps flailing in defence. Then on along a grassy path and down an embankment, stopping to investigate the umbels of giant hogweed for ants, flies, wasps and other insects taking advantage of this high-energy nectar source. A bit of a detour through the grass saw a flurry of sightings: common blue (Polyommatus icarus), small tortoiseshell (Aglais urticae) and a summer chafer (Amphimallon solstitiale). Unfortunately a bit early in the year for the now fairly well-established and easily recognisable wasp spiders (Argiope bruennichi), but I think another visit in late Summer should do the trick.

I dropped in at the visitor centre for a fruit juice and then headed off into the reed beds along the boardwalks where I saw a female scorpion fly (Panorpa sp.) with her particularly oddly-shaped extended mouthparts and chequered wing patterns. Here too, on thistle, were 6 hairy shieldbugs (Dolycoris baccarum) sporting Art Deco-like purple and green thoraxes, and black-and-white banding along their antennae and laterotergites. Disappointingly, I only managed to get one photograph of a dragonfly, a blue-tailed damselfly (Ischnura elegans) before closing time. And as I made my way to the exit marvelling at all the wonderful creatures I had been fortunate enough to see I was surprised by a female mallard leading her ducklings along the boardwalk who, on sight of me, dropped over the edge and disappeared into the reeds.

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